Corella, 1994, 18( 4): 125-129

THE MIGRATION OF BRIDLED TERNS Sterna anaethetus BREEDING IN WESTERN AUSTRALIA

J. N. DUNLOP 1 and R. E. JOHNSTONE2 1162 Swansea Street East. East Victoria Park. WA 6101 2Western Australian Museum, Francis Street, Perth. WA 6000

Received I March 1994

Bridled Terns breeding on the Western Australian coastline are generally absent from their nesting colonies and adjacent seas between early May and mid-September. The recovery of some marked terns banded at colonies in south-western Australia has now identified a definite 'wintering' area. This is located in the north-western sector of the , between about 4 and 7 degrees north latitude. Mixed flocks of adult and fledgling Bridled Terns observed moving through , Lintah Strait (between Flores and Komodo Is), and via the Sabu and Banda seas in the Lesser Sundas during April-May are considered to have been Western Australian birds on their post-breeding migration. Flocks observed in in August, September and October are probably birds returning to their Western Australian breeding grounds.

INTRODUCTION some information on the Bridled Tern migration. Observational evidence from a number of sources ln Western Australia 30-40,000 pairs of Bridled Sterna anaethetus provides some additional detail on the pattern of Terns breed on at least seventy movement. coastal islands from Lesueur I. ( I 3°50'S), in the ° north Kimberley. south to Seal Is. (34 23'S) in the STUDY AREAS AND METHODS south-west (R. E . .Johnstone and G. M. Storr, unpubl. data). Bridled Terns have been banded hy R. E. .Johnstone (RE.I) on North risherman Island (30°08'S. I l4°57'E: Fig. I) during The portion of this range south of the Houtman 14 breeding seasons between 1971 and the prcsenl. Over that Abrolhos Islands has been colonized since 1900 period approximately 800 birds (adults and pulli) have been and populations in this area continue to expand banded with CSIRO/A1313BS numbered metal rings. (Johnstone 1978; Dunlop and Wooller 1990; Banding was undertaken on Penguin Island (32°I7'S. Dunlop and Jenkins 1994). I I5°4I 'E: Fig. I) by .I. N. Dunlop (JND) and J. Jenkins. Some initial work was done in 1983. resumed in 1986 after a four year At almost all breeding colonies in Western break and continues to the prcscnl. Tu date 2169 13ridkdTerns Australia Bridled Terns arrive on their breeding ( 1493 adults and 676 pulli or llcdglings) have been handed on grounds between late September and mid­ Penguin Island. Details of capture and marking methods are October. The exodus, which involves the adults presented in Dunlop and Jenkins 1992 . As with North risher­ and the annual cohort of fledglings, usually takes man Island. Bridled Terns captured on Penguin Island carried place from early to mid-April. Bridled Terns a uniquely numhered CSIRO/ABBBS metal band. arc absent from the breeding islands, and from When recoveries were reported from outside Australian adjacent seas. between early May and mid­ waters. an attempt was made tO contact the finders in order September (Serventy er al. 1971; Storr 1984; Storr to retrieve as much information as possible. Finders were al. asked about the circumstances of the recovery and about the et 1986; Dunlop and Jenkins 1992). A north­ recovery environment. We also tried to glean any local ward migration has long been postulated for knowledge the finders may have had about Bridled Terns in Bridled Terns nesting on the Western Australian their area and about the harvesting of seabirds or the eggs. coastline, or at least for birds from the southern and mid-western colonies (Serventy et al. 1971). The initial recoveries indicated that Bridled Terns from colonies in Western Australia probably moved through This paper reports on the results of two banding Lombok Strait. and other straits in the Lesser Sundas. on studies in south-western Australia which provide route to their wintering area. Both authors attempted to

125 126 J. N. Dunlopand R. E.Johnstone: Migration of Bridled Terns Corella 18(4)

Sea 29 and 30 April 1991: strnit between Tilllor and Sem;1u ls and ,cas offSW Timnr 2 ;incl 8 May I 991: 13anda Sea (between 13amla and Kai ls) 30 September 1992: (between Kai and Aru ls) I and 9 October 19'!2: seas around Kai ls (including 1erong Slrait) 12 and 20 October 1992: seas off SW Tanimbar I.and strnil between Tanimbar andSclaru Is 25 and 29 April 1993 (Fig.2). R. Nujck provided ob,crvations from oil platforms in lite ° ° Timor Sea (.J.1biru Vcnlure I 1 55'33"S. 1 25 00'2J'E) and ° Challis Venture (12°07'17"S. 125 00'-IJ"E. Fig. 1).

RESULTS . Five Bridled Ternshanded at the study colonies 111 south-western Australia have been recovered 0,1 .,. outside of Australian waters. The basic band ,..,,._ returndetails from these recoveries arc presented in Table I. The recovery area is shown on Figure I and the specific locations are plotted on Figure 2. Although these returns involve birds from two colonies approximately 280 kms apart, span a period of 20 years and involve adults and first year birds. the recovery locations fall within a remarkably small and defined area. This lies between about 4 and 7 degrees north latitude in the north-western sector of the Celcbes Sea (Table I. Fig. 2). Four of the five recoveries (3 adults. I year 0) Figu1c· I ..\la11 owli11,• of i\11srmlia all(/ r!,c lndo-l'acific regions were from the austral winter period when Bridled 1/urn·i11g r!,c loca1io11 of 1/,c 111·0 ha11di11g .,·tatiom a11d the rcg11111 111 1/,c 11orrh-11·,,s1cm Ce/ch,,.,. S('// fi-0111 "'hie!, Terns are known to be absent from the seas rc•co,·crit·, hal't' hc,·11 reported. Al,·o shou·n i,\ tltc p1J\itio11 of adjacent to their breeding islands. One tern in its till' oil 11/(l{jor1111 111,·111io111'd i11 the l<'XI. first year of life was recovered at the southern­ most locality in December (Table I). oh,ervc thl' Pt"t•hn:cding migration through LomhokStraight u,ing travcr,c, 011 commercial ferric, (Rl:J on I and '.ll May All three adults recovered were captured alive 1'!88 and .IND 1111 2 and<, �la\' 1993). and in probably all these cases the terns were at DL'tail, of othn ,ca-cro"ing, hy REJ in ferries and tbhing sea. or at least some distance from shorelines. boats .trl.' a, follow,: Ala, Strait (hc·twccn Lornbok and One bird (061-23362) was a member of a group Sumhawa I,) 7 and 211 t--tav and 18 October 1988: ,trait of seven roosting at night on tloating coconut hct\\'ccnSumhawa and San1!�anc Is 21 and D October I 988: shells (Adclma Calunsag. pcrs. comm.). Another ,c·;1, around Sulllhawa and �IOI'<; h <, and 14 November 1988: (061-77422) alighted at night on a small fishing strait bct11c·cn Tinrnr and Scm:1u i, 22 October 1989: Flores. SPl01 and Lalllakera Straits (bctwccn Flore,. Adonara and boat about 240 km from land (Manolito Antipolo, l,e111h;1ta Is) I No\'Clllhcr 11181): L11nakcra Strait (between pcrs. comm.). Both of these recoveries were Lcmbata and Adonara I,) 12 Novclllbcr 1989: Flore, Strail 1-l probably dazzled by ship lights. No\'cmhc1 1989: t--tolo Strait (between Flores and Rinca I,) 12 and l:i :-.ta) 1990: ,ca, and Linlah Strait (hctwccn Flore, The period from June to August is the fishing and Ko111odo t,)17. 20 and 22 May 1990: strait between Tilllor season for the comrnen.:ial boats operating in the and Scmau I, 21{ and_"\() :-.ta} and 20 and 25 October 1990 and Celcbes Sea from southern Mindanao (Adelma 7 ,\pt Ii 1991: R,111 Strait (bct\\'ccn Tilllor and Roti Is) 25 Calunsag. pers. comm.). This presumably corres­ Scplc111he1. 5 October and 18 October 1990: Sahu Sea ponds to the peak season in marine productivity (hct11·c,·11 rimor and Sahu h) 26 September and -I October in the region. Bridled Terns arc referred to as j

TABLE I Basic band return data fur Bridkd Ternsmarked on either North f-'ishennan or Penguin Island and recovered in the lndo-Pacitic region.

Recovery Recovery Distance (km) Band No. Colom· Date Age co-ordinates date /bearing

° ° ° 1)61-1111170 North Fisherman 7 Jan. 197:\ Year 0 3 52'N. 117 .JO'E 28 Dec. 197:\ Yi-lO. 0 ° ° ° '.\1orthFisherman 3 I Dec. 1979 Year 0 5 09' N. I 19 1YE 18 /\ug.1980 383.J.0 ll61-212n ° ° ° Penguin Island I "1ov.I 986 2+ 6 55' N. 122 05' E 20June 1991 .J305. 12 1161-23362 ° ° ° .122 Penguin Island 7 Oct. 1988 2+ 4 30'N. 122 -lO'E 11 July 1992 .j 155.· 12 ()61-77 ° ° ° (l(i \-2 I 290 North Fisherman 5Jan.l':181 2+ 5 01'N. 119 -16'E 15 June 1993 39-11. 8

it at the sea· (Manolito Antipolo (sic). pers. on 30 April 1991: small Aocks (up to 6) off Roti I. comms.). This informant was aware of other nest­ and between Roti and Ndana ls in October 1990; ing terns referring to ·some of the birds do nest Aocks of 50, 52 and 6 off SW Tanimbar I. on 20 on islands in the trees·. Presumably these were April 199:1: and flocks of 10, 54. 100. 20 and 15 Black Noddics A11011s 111inw11s. in strait between Tanimbar and Sclaru Is in late April 199:1. On I May 1988. REJ observed three mixed flocks of adult and juvenile Bridled Terns feeding and Details of observations by R. Nojck from oil moving north through Lombok Strait (Johnstone rigs in the Ti1nor Sea arc as follows: 1-14 March er al. 199:1). However, there was no evidence of 1988, 6- l0bircls per day: 16-29 August 1988. 6-10 passage movement when JND crossed the strait birds per clay ; 25 April-I May 1989. 10-12 birds on 2 and 6 May 199:1. Details of other observa­ per clay; 24-29 September 1989. c. Ill() birds per tions in the Lesser Sundas by REJ are as follows: clay; 10-17 October. 1989. 50-100 birds per clay; One dead immature on Pasir I. on 20 May 1990: 12-25 January 1990, 4-6 birds per clay: 18-21 small flocks (up to 6) off Komodo 1. on 22 May April 1990, 10-:10 birds per day. Adults and 1990: flock of 6 near Sernau I. on 28 May 1990; juveniles were observed most months. flocks of 8. 10 and 20 between Kupang and Semau I. in September-October 1990: one just off Kera I. DISCUSSION

140"!. Bridled Terns breeding at North Fisherman Island and Penguin Island during the austral summer spend the austral winter in the north­ western sector of the O: lcbes Sea (Fig. I). Breeding adults and their fledglings leave their nesting colonies in Western Australia in loose flocks. usually vacating the islands by mid-April to early May. although delays have been observed L in some years. Between late April and late May similar flocks were observed moving northwards through Lombok Strait. Lintah StraTt and via the Sabu and Banda Seas. The fledglings with these flocks identified them with the breeding schedule in Western Australia. Breeding in the 1992/93 !..ol. season was delayed in Bridled Tern colonies in south-western Australia. and as far north as the Dampier Archipelago. This may explain the absence of terns in passage in early May 199]. Figure 2. lv/ ap of rh(' /111/o-!'11nfir Rer;irm sho11·i11g rhe lon11io11s The northward migration appears to be a fairly i11 rhc Ce/('hCs Sea ar 11·/,ich ji i·e /} (uult'd Hridled Tems ll'('ff leisurely movement with the terns feeding along ffco,·acd I•) and also the passages through Wallacea the way. A similar post-breeding ·mass· migration where the,c ternshaw been observed on migration. has been observed on the cn;ist of Sri Lanka near 128 J. N. Dunlop and A. E. Johnstone: Migration of Bridled Terns Corella 18(4)

Colombo. presumably involving Bridled Terns arc utilising a space in local Bridled Tern distribu­ moving southwards from breeding colonies in the tion. Further west, off Sabah and northern Arabian Gulf to wintering areas on the equator Kalimantan and south of the Sulu Islands, this (De Silva 1987). Ternsfrom the Red Sea colonies may not be the ca c (e.g. extant colonies are arc known to move in August southwards down recorded from : De Korte 1991). the cast coast of Africa as far as Mozambique There is no evidence that adult Bridled Ternsare (Cramp 1985) in another comparable migration. harvested and none of the recoveries to date 8ridled Terns from Western Australia making involve birds taken for food. However. the passage through the Lesser Sundas almost certainly reduction in local breeding colonies caused by egg complete their journey to the wintering area via harvesting may have favoured migratory popula­ Makassar Strait. presumably from the second half tions by relaxing competition for food in the of May to early June. The recoveries indicate that wintering area. Such a change could possibly the adults at least. are only present in the north-· contribute to the expansion of Bridled Tern western Celebes Sea in June. July and August. populations in south-western Australia. One first year tern was recovered in the area in In Wallacea the Bridled Tern·s present status December which may indicate that not all birds in unclear. breeding is recorded on Gunung Api make the return migration for their second year. Bridled Terns in this age class have been recorded in July-August. probably also Sangi Sangiang at the Penguin Island and Fisherman Island (White and Bruce 1986) and from islands south of Lombok (De Korte 1991). Judging from our colonies but they arc rare. Pre-breeding birds ( I-] year olds) also appear at the Penguin Island observations in this region there is some breeding colony later in the season than the more experi­ but most birds arc passage migrants to and from enced individuals. and it is possible that the Australia. younger terns trail the adults on the returnmigra­ tion (Dunlop and .Jenkins 1992). This may also ACKNOWLEDGMENTS explain the late (September/October) movements observed through the Timor Sea. The timing of The handing of 13ridlcd Tern, was carried out under the auspice, of the Au,tralian Bird and Bal 13anding Scheme. The arrival at the colonies would indicate that the rrc­ ANCA ,1aff of the Schem.; abo provided original corn.:spon­ breeding migration takes place during late August

Dunlop. J. N. and Jenkins. J. (1994). Population dynamics of St0rr. G. M. (1984). Birds of the l'ilbara Regions. Western the 13ridlcd Tern S1erna a11ae1J,e111s colony on Penguin Australia.Records of the Western Australian Museum. Island. south-western Australia.Corella 18: 33-36. Supplement No. 16. p.34. Dunlop. J. N. and Woollcr. R.D. ( 1990). The breeding sea­ Storr, G. M .. Johnstone. R. E. and Griffin. P. (1986). Birds birds of south-western Australia: trends in species. popula­ of the I loutman Abrolhos. Western Australia.Records tions and colonies.Corella 14: 107-112. of the \V estern Australian Museum. Supplement No. 24. I larrison. P. ( 198J). ·seabirds: An identification guidc. · p. 33. (Croom-Hehn: Beckcnham.) Wells. D.R. ( 1991). Status and conservation of seabirds Johnstone. R. E. (1978).Seabird Islands No. 64. North breeding in Malaysian waters.In: ·supplement lo the Status Fishcnnan Island, Western Australia. Corella 2: 43-47. and Conservation of the Worlds Seabirds.· ICl3P Technical Johnstone. R.E .. van Balcn. S. and Dekker, R. J.( 1993). New Publication No.11 . 213-223. hird records for the island of Lombok. Kukila 6(2): 124-128. White, C.M. N . and Bruce. M. D. (1986).The Birds of Scrvcnty. D. L. . Serventy.V. and Warlw111. J. (1971).·The Wallacea (Sulawesi. the Moluccas and Lesser Sunda Handbook of Australian Seabirds.· (A. H.and A.W. Recd: Islands. ). An annotated checklist. B.O.U. Sydney.) Checklist No. 7.

Comparison of the diet of breeding and non-breeding Cape LITERATURE REVIEW Gannets Morus capensis. Berruti. A.(1 991).Os1rich 62: 8- -12. (Regurgitations obtained from breeding gannets were heavier and contained more prey than those from non-breeders. Compiled by D. Purchase, D.Murray and B.Baker. Therefore the mean energy content of the regurgitations was significantly greater.) This section is compiled from journalswhich arc often not available 10 non-professional ornithologists in Australia.The Long-range movement of a Cape Gannet Marus capcnsis in the following criteria arc used 10 select papers for review: southern . Bertcaux. D. ( 1991). Marine Omi- 1/,0/ogy 19: 134-135.(Flt :dgling banded in South Africa live • They n: lalL· to species which occur in Australia and its years previously sited on empty nest. and in subsequent year Tcrritoric�: on own nest in middle of breeding colony of Yellow-nosed Albatrosses on Amsterdam Island). • Thev provide details of tcchniques and equipment that may Cormorants Phalacrocorax carbo at cage fish farms in Argyll. he of use in Australia: western Scotland. Carrs. D. N. (1993). Seahird 15: .18�-l (Brids did not take fish but attacked them through the netting • They provide details of studies that may be of general causing fatal wounds.) interest to Australian ornithologists. Diving patterns and performance in male and femaleBlue-eyed Journals perused: /\rdea 80: Auk 108, 109. 110: Condor 95: Cormorants Phalacrocorax atriccps at South Georgia. Kato. t:Oise1111 RFU. 61: Marin<' Omi1hology 19: Nonh A111erirn11 A. el al.( 1991). Ma rine Omirhologr 19: 117-129. (The divin!! lJwu/er 16: No1omis 38, 39: Ostrich 62: Seahird 15: Wildlife patterns of two males and one female were recorded with lfrs('{lrc/, 20: Wil.w11 /111l/c1i11 104: World /Jird,rnrcl, 13. continuous-recording time-depth recorders for 10-13 days.) f-ood supply and allocation of parental effort in Arctic Terns Sternaparadisaca. Uttley. J. D. ( 1992).Ardea 80: (The alloca­ C,ENER/\1. INTEREST tion of effort between sexes during breeding changed in response to c11virunn1e.:nt